Indenting heredocs with spaces [duplicate]

Answer 1

geta() {
  local _ref=$1
  local -a _lines
  local _i
  local _leading_whitespace
  local _len

  IFS=$'\n' read -rd '' -a _lines ||:
  _leading_whitespace=${_lines[0]%%[^[:space:]]*}
  _len=${#_leading_whitespace}
  for _i in "${!_lines[@]}"; do
    printf -v "$_ref"[$_i] '%s' "${_lines[$_i]:$_len}"
  done
}

gets() {
  local _ref=$1
  local -a _result
  local IFS

  geta _result
  IFS=$'\n'
  printf -v "$_ref" '%s' "${_result[*]}"
}

This is a slightly different approach which requires Bash 4.1 due to printf's assigning to array elements. (for prior versions, substitute the geta function below). It deals with arbitrary leading whitespace, not just a predetermined amount.

The first function, geta, reads from stdin, strips leading whitespace and returns the result in the array whose name was passed in.

The second, gets, does the same thing as geta but returns a single string with newlines intact (except the last).

If you pass in the name of an existing variable to geta, make sure it is already empty.

Invoke geta like so:

$ geta hello <<'EOS'
>    hello
>    there
>EOS
$ declare -p hello
declare -a hello='([0]="hello" [1]="there")'

gets:

$ unset -v hello
$ gets hello <<'EOS'
>     hello
>     there
> EOS
$ declare -p hello
declare -- hello="hello
there"

This approach should work for any combination of leading whitespace characters, so long as they are the same characters for all subsequent lines. The function strips the same number of characters from the front of each line, based on the number of leading whitespace characters in the first line.

The reason all the variables start with underscore is to minimize the chance of a name collision with the passed array name. You might want to rewrite this to prefix them with something even less likely to collide.

To use in OP's function:

gets usage_message <<'EOS'
    Hello, this is a cool program.
    This should get unindented.
    This code should stay indented:
        something() {
            echo It works, yo!;
        }
    That's all.
EOS

usage() {
    printf '%s\n' "$usage_message"
}

As mentioned, for Bash older than 4.1:

geta() {
  local _ref=$1
  local -a _lines
  local _i
  local _leading_whitespace
  local _len

  IFS=$'\n' read -rd '' -a _lines ||:
  _leading_whitespace=${_lines[0]%%[^[:space:]]*}
  _len=${#_leading_whitespace}
  for _i in "${!_lines[@]}"; do
    eval "$(printf '%s+=( "%s" )' "$_ref" "${_lines[$_i]:$_len}")"
  done
}